Substrate-free crystalline 2d bismuthene

ABSTRACT

The present disclosure generally relates to compositions comprising substrate-free crystalline 2D bismuthene, and the method of making and using the substrate-free crystalline 2D bismuthene.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefits of U.S. Provisional ApplicationSer. No. 62/776,046, filed Dec. 6, 2018, the contents of which areincorporated herein entirely.

TECHNICAL FIELD

The present disclosure generally relates to compositions comprisingsubstrate-free crystalline 2D bismuthene, and the method of making andusing the substrate-free crystalline 2D bismuthene.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

Research in 2D materials, as inspired by the development of graphene,has experienced an explosive increase in recent years, due to theirunique and exceptional properties with promising applications inelectronic, photonic, energy and environmental devices. The 2D group-IVmaterials including silicene, germanene and stanene have been realizedexperimentally after graphene. For group-V elements, few-layer blackphosphorus, named phosphorene, has also been successfully fabricated byexfoliation, which exhibits prominent properties such as high carriermobility and high on/off ratio.

Although 2D bismuthene and its potentially important features andapplications important have been reported, the reported 2D bismuthenehas to be supported on a substrate. See Reis, F., et al., Bismuthene ona SiC Substrate: A Candidate for a New High-Temperature Quantum SpinHall Paradigm, Science 357, 287-290 (2017). Thus, the applications of 2Dbismuthene materials are greatly hindered.

Therefore, there remains a need to develop a method to makesubstrate-free 2D bismuthene due to its potential applications inelectronics, optoelectronics, energy conversion and energy storage.

SUMMARY

The present disclosure provides compositions comprising substrate-freecrystalline 2D bismuthene, and the method of making and using thesubstrate-free crystalline 2D bismuthene.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene.

In one embodiment, the present disclosure provides a method of preparingsubstrate-free crystalline 2D bismuthene, wherein the method comprisesreductive reaction of NaBiO₃ with a capping polymer and a polyol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows optical image of the as-prepared 2D bismuthene.

FIG. 2 shows atomic force microscopy (AFM) image of a single 2Dbismuthene triangle nanoflake.

FIG. 3 shows an atomic-thin 2D bismuthene with 4.18 nm thickness.

FIG. 4 shows Transmission Electron Microscopy (TEM) image of a single 2Dbismuthene triangle nanoflake with the Selected Area Diffraction (SAED)as the inset obtained by aligning the electron beam perpendicular to thesurface of the 2D bismuthene nanoflake.

FIG. 5 shows High Resolution Transmission Electron Microscopy (HRTEM)image with clear lattice fringes that confirm the highly crystallinenature of the as prepared 2D bismuthene.

FIG. 6 shows the typical 2-theta XRD pattern of the as-prepared 2Dbismuthene nanoflakes.

FIG. 7 3D illustration of the structure of the 2D bismuthene.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of this disclosure is thereby intended.

In the present disclosure the term “about” can allow for a degree ofvariability in a value or range, for example, within 10%, within 5%, orwithin 1% of a stated value or of a stated limit of a range.

In the present disclosure the term “substantially” can allow for adegree of variability in a value or range, for example, within 90%,within 95%, or within 99% of a stated value or of a stated limit of arange.

In the present disclosure, the term “2D bismuthene” refers to anallotrope of bismuth element. The term “2D bismuthene” refers theallotrope in the form of two-dimensional, atomic scale, and hexagonallattice. One well-known 2D material is graphene, which is an allotropeof carbon.

In the present disclosure, the term “substrate-free 2D bismuthene”refers to 2D bismuthene crystals that are prepared through a solutioncondition instead of being deposited on a substrate as disclosed byReis, F., et al. regarding 2D bismuthene on SiC substrate. Thedisadvantage of 2D bismuthene on substrate is that such material cannotbe easily used and is not available as standalone 2D bismuthene crystal.Therefore, the substrate-free 2D bismuthene disclosed in the presentdisclosure provides a standalone, stable and convenient source of pure2D bismuthene. A skilled artisan will appreciate that “substrate-free 2Dbismuthene” refers to “substrate-free 2D bismuthene” as made. The laterprepared composition by any other physical and/or chemical mixing orcombining the as made “substrate-free 2D bismuthene” with anothermaterial, even could be named as “substrate”, should still be within thedefinition of “substrate-free 2D bismuthene” as defined here.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene nanoparticles.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene nanoflakes.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene having single crystalline nature.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene nanoflakes having substantially equilateraltriangle shape. In one aspect, the length of each side of thesubstantially equilateral triangle shape is 0.1-100 μm, 0.1-80 μm,0.1-60 μm, 0.1-40 μm, 1-100 μm, 1-80 μm, 1-60 μm, 1-40 μm, 10-100 μm,10-80 μm, 10-60 μm, 10-40 μm, or any combination thereof.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene nanoflakes having single or multilayerstructure with a thickness of 0.1-30 nm, 0.1-20 nm, 0.1-10 nm, 0.1-5 nm,0.1-3 nm, 1-30 nm, 1-20 nm, 1-10 nm, 1-5 nm, 1-3 nm, or any combinationthereof.

In one embodiment, the present disclosure provides substrate-freecrystalline 2D bismuthene nanoflakes that are characterized by an X-raydiffraction pattern (CuKα radiation, λ=1.54056 A) comprising a peak at26.16 (2θ±0.10), and optionally one or more peaks selected from thegroup consisting of 36.99, 38.64, 47.67, and 55.14 (2θ±0.10).

In one embodiment, the present disclosure provides a method of preparingsubstrate-free crystalline 2D bismuthene nanoflakes, wherein the methodcomprises reductive reaction of NaBiO₃ with a capping polymer and apolyol. In one aspect, the polymer may be but is not limited topoly(vinylpyrrolidone) (PVP, MW1 300 000), the polyol may be but is notlimited to ethylene glycol.

In one embodiment, the present disclosure provides a method of preparingsubstrate-free crystalline 2D bismuthene nanoflakes, wherein the methodcomprises:

dissolving the capping polymer in the polyol to form a mixture of thecapping polymer and the polyol;

heating the mixture to an elevated temperature for a period of time andthen cooling the mixture to ambient temperature;

adding NaBiO₃ to the mixture of the capping polymer and the polyol, andheating the newly formed mixture to an elevated temperature for a periodof time; and

cooling the reaction mixture to ambient temperature to provide thesubstrate-free crystalline 2D bismuthene nanoflakes.

Synthesis of Crystalline 2D Bismuthene Nanoflakes

The crystalline 2D bismuthene nanoflakes with substantially uniformshape were prepared by a polyol process. The primary reaction involvedthe reduction of NaBiO₃ (99.6%, Aldrich) with ethylene glycol (EG,99.8%, Aldrich) in the presence of the capping polymerpoly(vinylpyrrolidone) (PVP, MW1 300 000) (Aldrich). First, 0.1472 g PVP(MW 1300000) was dissolved into 40 mL EG with strong stirring withtemperature raising up to 100° C. for 7 hours. After the whole solutioncooling down to room temperature, 0.412 g NaBiO₃ were added into abovesolution with vigorous stirring for another 8 hours. We can see thesolution become light yellow. Then, we can pour this light-yellowsolution into a 50 mL Teflon-lined stainless-steel autoclave.Consequently, the autoclave was sealed and maintained at 180° C. for 20hours. The autoclave was then cooled to room temperature naturally. Theresulting yellow products were precipitated by centrifugation at 5,000r.p.m. for 5 min and washed three times with distilled water (to removeany ions remaining in the final product).

XRD Patterns of the Crystals

The XRD patterns of the crystals are obtained on a D8 Advance X-raypowder diffractometer, equipped with a CuKa source (λ=1.54056 A) and aVantec detector, operating at 40 kV and 40 mA. Each sample is scannedbetween 20° and 65° in 2θ, with a step size of 0.0057° in 2θ and a scanrate of 11.41 seconds/step, and with 2.1 mm divergence and receivingslits and a 0.1 mm detector slit. The crystalline 2D bismuthenenanoflakes are deposited on the Si wafer with smooth surface. Thecrystal form diffraction patterns are collected at ambient temperatureand relative humidity. The background for the crystal is removed by Jade6.5 prior to peak picking.

Conformation of a crystal form may be made based on any uniquecombination of distinguishing peaks (in units of ° 2 θ), typically themore prominent peaks. Thus, a prepared sample of crystalline 2Dbismuthene nanoflakes is characterized by an XRD pattern using CuKaradiation as having diffraction peaks (2-theta values) as demonstratedin Table 1.

TABLE 1 X-Ray Crystal Diffraction Peaks of crystalline 2D bismutheneAngel °2 θ Intensity Ratio (012) Crystallographic plane 26.16 1.00 (012)36.99 0.39 (104) 38.64 0.39 (110) 47.67 0.24 (202) 55.14 0.19 (024)

FIG. 1-7 provided optical images/data of the as prepared 2D bismuthene.The optical image FIG. 1 clearly indicated the morphology of theas-synthesized 2D bismuthene. Each 2D bismuthene nanoflake has anequilateral triangle shape with length of the 20-30 um side length.Atomic force microscopy (AFM) verified the nature smooth of 2Dbismuthene surface. FIG. 2 and FIG. 3 showed an atomic-thin 2Dbismuthene with about 4.18 nm thickness. FIG. 4 showed the TEM image ofa single triangle nanoflake with the SAED as the inset obtained byaligning the electron beam perpendicular to the surface of the 2Dbismuthene. The hexagonal symmetric diffraction pattern indicates thesingle crystalline nature of the nanoflake. FIG. 5 showed the HRTEMimage with clear lattice fringes that confirm the highly crystallinenature. The spacing of 0.23 nm and 0.13 nm corresponds to the (2-1-10)and (01-10) panes of 2D bismuthene. FIG. 6 showed the typical 2-thetaXRD pattern of the as-prepared 2D bismuthene nanoflakes. All diffractionpeaks were indexed to the rhombohedral Bi structure (JCPDS No. 05-0519,R-3m). The inset is the schematic of the rhombohedral lattice structureof bismuth belonging to space group R-3m, together with the hexagonalunit cell. (thin lines) The 3D schematic image in FIG. 7 indicates thatthe sample grow laterally along the <01-10> and <2-1-10> directions,with vertical stacking along <0001> direction.

In summary, a simple, low-cost, solution-based chemical pathway to thescalable synthesis and assembly of substrate-free 2D bismuthene wasdeveloped. This approach has the potential to produce stable,high-quality, ultrathin semiconductors with a good control ofcomposition, structure, and dimensions for applications in electronics,optoelectronics, energy conversion, energy storage, sensors, and quantumdevices. The substrate-free 2D bismuthene therefore adds a new class ofnanomaterials to the large family of 2D materials and enablespossibilities for the further investigation of many exciting propertiesand intriguing applications.

2-D bismuthene is predicted to be 2D topological-insulator (quantum spinHall) at high-temperatures (potentially even close to room temperature)that would facilitate the practical deployment of topological and hybridelectronic quantum materials. Due to the intrinsic spin-orbit coupling,bismuth is a promising candidate in spintronic devices with no demandfor an external strong magnetic field. Bulk bismuth is a semi-metal,while 2-D bismuthene with the thickness thinner than the Fermiwavelength could see a transition from semimetal to semiconductorbecause of the quantum confinement effect.

2-D bismuthene could also be a good thermoelectric material, aphotothermal material for potential photothermal treatment ofcancer/tumor cells in vivo, exhibits diverse promising applications inelectronics, optics, thermoelectricity, superconductivity, and as acandidate for a new high-temperature Quantum Spin Hall paradigm, etc. inquantum electronics.

Those skilled in the art will recognize that numerous modifications canbe made to the specific implementations described above. Theimplementations should not be limited to the particular limitationsdescribed. Other implementations may be possible.

1. A composition comprising substrate-free crystalline 2D bismuthenenanoflakes.
 2. The composition of claim 1, wherein the crystalline 2Dbismuthene nanoflakes have single crystalline nature.
 3. The compositionof claim 1, wherein the crystalline 2D bismuthene nanoflakes havesubstantially equilateral triangle shape.
 4. The composition of claim 3,wherein the length of each side of the substantially equilateraltriangle shape is 0.1-100 μm.
 5. The composition of claim 1, wherein thecrystalline 2D bismuthene nanoflakes have multilayer structure with athickness of 0.1-30 nm.
 6. The composition of claim 1, wherein thecrystalline 2D bismuthene nanoflakes are characterized by an X-raydiffraction pattern (CuKα radiation, λ=1.54056 A) comprising a peak at26.16 (2θ±0.1°), and optionally one or more peaks selected from thegroup consisting of 36.99, 38.64, 47.67, and 55.14 (2θ±0.1°).
 7. Amethod of preparing substrate-free crystalline 2D bismuthene nanoflakes,wherein the method comprises reductive reaction of NaBiO₃ with a cappingpolymer and a polyol.
 8. The method of claim 7, wherein the methodcomprises steps: dissolving the capping polymer in the polyol to form amixture of the capping polymer and the polyol; heating the mixture to anelevated temperature for a period of time and then cooling the mixtureto ambient temperature; adding NaBiO₃ to the mixture of the cappingpolymer and the polyol, and heating the newly formed mixture to anelevated temperature for a period of time; and cooling the reactionmixture to ambient temperature to provide the substrate-free crystalline2D bismuthene nanoflakes.
 9. The method of claim 7, wherein the polyolis ethylene glycol, the capping polymer is polyvinylpyrrolidone (PVP).